A Rat in the Sewer
by World Ink
Summary: Dr. Falco is alive, and prepared for his own retribution. He has a plan to rip the turtles out of the sewer by their roots – and slowly, the pieces are coming together. The only problem is fighting an enemy who has your mind at his disposal.
1. Infestation

**A Rat in the Sewer**

* * *

Summary: Dr. Falco is alive, and prepared for his own retribution. He has a plan to rip the turtles out of the sewer by their roots – and slowly, the pieces are coming together.

* * *

**Chapter One: Infestation **

Dr. Falco's damaged skin was burlap, drumming his fingers together idly while he thought. Murky shadows smeared across his face, highlighting the torched features and allowing his crimson eyes to glow in the darkness with an uneven hue. His face was contorted further by the intense focus wracking his expression, his mind preoccupied with an intense hatred. The main concentration of his disgust was, naturally, the turtles. They had ruined _everything _for him, and had experienced little consequence to their actions. His loathing for them was graceful, almost, in the way it intertwined itself to his every thought, like some twisted dance that constantly twirled in his mind.

Most men, at this point, would have come to the conclusion that giving up was the only option left - but he had always considered himself a man of patience and determination. In fact, if anything, the recent defeat had only furthered his resolve. He would get his revenge, and the turtles would suffer at his hand. He would personally rip their screams from their throats, make them experience and endure a pain equivalent to his own. He smiled at the thought of dissecting them, wielding a scalpel and slicing them apart, one by one.

Yet, the latest wound sat painfully on his mind. They'd _still _managed to beat him, wriggling out of fate's hand like water in a clenched fist. Justice had been evaded that day, and the promise revenge had betrayed him. He'd literally had their master at his side, and they'd gotten _away_.

He felt anger curdle his blood into a boiling slush, just at the thought of it – he'd been _so close_. Splinter's blade had nearly struck Leonardo down, but then the brothers had tackled him working together and breaking the rat out from under Falco's telepathic grip.

Suddenly inspiration struck, cracking a smile across Falco's face like a shattering glass - that was _it_. He'd had their _master_ under control, but they'd still had each other. The solution was painfully obvious. He needed to separate the turtles at their core – he supposed that if he could manage to take down just one, the whole team would come crashing to its knees. And he knew just the one.

Donatello – that was the one he hated more than any of them. Even at the thought of his name, anger nibbled on his mind like the rats gnawed at his cloak, and his fists clenched.

Literally without even thinking, he'd taken down years of study and months of careful planning. Within the span of a few seconds, the young genius had ripped away from Falco an entire future, setting the groundwork of his plans to flame without a single thought. In a single night, he had dismantled years of meticulous research and careful preparation - literally without even thinking, he'd beaten Falco at his own game.

He wanted to make him suffer, to make him and his brothers feel pain equivalent to his own.

A plan was blooming in his brain like a flower snagged in thorns, nurtured by seeds of abhorrence and nourished with the promise of retribution.

Carefully, Falco stood up, raising his hands to his temples as he braced himself for mental exhaustion as he tested out his telepathic abilities – sure enough, he felt the mental hums coming from fifteen or so rats. He kept his influence close at hand, not wanting to alert Splinter's wary mind to his plans. The mutant rat was why he had been reluctant to push out too many orders to his furry servants. But the days of his hiding were coming to an end.

"_To me, my brothers,"_ He mentally whispered to the rats in his range, "_I am in need of you."_

Within the span of minutes, he was surrounded by eighteen rats that had scurried over and lined up in front of him. Curious, beady, black eyes glittered up at him, squeaks hammering against his ears like the inflection of music.

"_Very good, my sons and daughters," _ Falco praised, his maddened grin widening to reveal his gravestone teeth, "_You have done well, it's true. It was you who saved me from capture – and though that was not long ago, I am once more in need of your assistance."_

Noses twitched at him, shrill chattering filling the air in what, to Falco's mind, sounded like confusion. To counter their befuddlement, he raised his arms out them in what he hoped was a comforting manner.

"_I have a plan in place, one with which we will finally destroy the turtles. But first, brothers, you must aid me. Find the turtle's lair, locate Donatello, and then report back to me_. _You will be my eyes and ears, my precious brothers,_" His eyes glowed in anticipation, "_Now, be on your way!"_

Orders given, the rats turned, racing down the maze of the sewer passages they knew so well.

Pleased with himself, the scientist cracked his knuckles before climbing back up into the unused sewage pipe he'd woken up in weeks before. His bones cracked and shuddered like worn-out gears as he bent his body back up to fit. Still, not even the biting chill of the cold metal could dampen his spirits, and his teeth clicked together menacingly in delight.

"Enjoy your will while it is still your own, turtles," Falco murmured to himself quietly, an insane tint to his smile.

* * *

The recent infestation of rats was annoying, to say the least. The turtles were used to a rat or two wandering into lair every once in a while – they lived in a sewer, and some things were simply unavoidable. However, the past week or so had been far past overkill. The furry little rodents were quite literally _everywhere_ – Leo had been disappointed to find the cable cords to the television chewed through, Mikey had numerous indentions in his nunchucks that had been left by rat teeth, and Raph had found a rat banging mercilessly on Spike's shell as he tried to open it and find the turtle inside. Needless to say, all three of the brothers had been less than pleased.

Donatello hadn't been entirely delighted with the situation either – the rats had made a habit of gnawing away at his stray wires and circuit boards, which were hard to replace. Not only was that, but the added work load of repairing what the rodents dismantled starting to drive him up the wall.

All he could fathom was that after Falco had directed almost the entirety of the rat population into the sewers, they'd simply stayed. He felt almost sorry for them, but his pity was quickly running out as he painstakingly rearranged the wiring in the cable cord and fastened three layers of strong rubber wire tape over the exposed wiring, hopefully making it chew-proof.

Job done, he leaned back, wiping sweat from his forehead as he peered back from behind the television at Leo, who had his finger on the power button of the television.

"Okay Leo, try it out." Donnie said.

Pressing the button, the TV shot to life in a roar of static. The screen flickered a couple times, but then the picture cleared and the sound reoriented itself. Leo grinned, giving Don a thumbs-up.

"Great work, Donnie." Leo started to say, just before a rat skirted out from under the set in a mass of panicked squeaks, and his gaze flattened, "Geez, what are we going to do with all these rats?" he muttered, and Donnie shrugged.

"I heard Raph saying something about a new fireplace rug." The purple-banded turtle offered.

"Do we even have a fireplace?" Leo asked, a grin appearing on his face.

"Raph doesn't let facts get in the way of things," Donnie replied, mirroring the bemused expression on his brother's face.

Leo stood u, and offered his hand out to Donnie as he helped him to his feet, examining the television warily.

"That's the second time in the past three days you've had to patch that thing up," the leader stated with a frown, "This is getting ridiculous!"

Donnie nodded in agreement, "You know Mikey's actually started putting pizza in the fridge when he's done?"

Leo's mouth dropped open, "Really?"

"Yeah, he's tired of the rats finishing it off before he can."

Leo sighed, a feeling of defeat rolling over him briefly, "Wow, this infestation is getting serious if _Mikey_ is willing to start picking up after himself."

"Yeah…You know, with some minor adjustments to the toaster, I think we could solve this problem in two days flat," Donnie mused, only half joking.

Leonardo crossed his arms at the quip though – for all his lighthearted teasing, he could tell Donnie was starting to get tired. Not that it was all that surprising. Their resident genius hardly slept as it was, always tinkering around on the computer or working on the Shellraiser – but with the recent onslaught of rodents, Donnie had been pushed into overdrive with an extra amount of work added to his plate. He'd been unintentionally assigned to fixing a majority of what the rats chewed up; and frankly, there wasn't much Leo could do to lift the burden from Donnie's shoulders. He worked like a horse anyway, and no one else was entirely equipped to rewire the electricity, fix the toaster, or anything else Donatello had taken upon himself to do. Still, Leo didn't like the dark rings that were starting to appear under his younger brother's eyes.

At the same time, if he questioned Donnie on it, he would deny that the extra workload was getting to him. In fact, he might even push himself harder to prove just how fine he was, and Leo wasn't prepared to deal with _that_ on top of everything else.

The mental back-and-forth had caused him to pause for a bit longer than usual, he noticed Donnie looking at him curiously as he waited for a response.

"Er, one thing at a time," Leo responded, "Has April gotten those mouse traps for you yet?"

Donnie nodded, rolling up the electrical tape to be used again as he turned back to the TV, "Yeah, Raph and Mikey are setting them up right now, I think-"

"_OW!_" A scream jutted out unexpectedly, causing both brothers to jump. Startled, Leo turned around to see Raph walking into the room with a barely contained smirk on his face. Right behind him, Mikey walked in, his index finger hidden in his mouth and a pained expression on his face. Both of them took a seat on the couch facing the television.

"What happened to you?" Leo asked, gesturing to Mikey who still appeared to be nursing the wound.

"Got his finger stuck in a mouse trap." Raph responded immediately, and managed to maintain his composure for almost three seconds before erupting into a fit of giggles. Mikey glared at him, punching his older brother with his uninjured hand.

"Ift's notff funny!" Mikey interjected lamely, finger still rolled into his mouth.

"You're right," Raph laughed excitedly, "It's hilarious!"

Leo couldn't help but smile as Mikey pulled his hand out of his mouth long enough to stick his tongue out at Raph before replacing the injured in its hiding spot.

Donnie chuckled, shaking his head before standing up, the tool kit he'd brought over fully packed and latched in his hand.

"If you guys need me, I'll be in the lab," The tallest turtle excused himself, leaving Raph and Mikey to fight amongst themselves.

Leo checked the clock on the lairs wall – he was surprised to see it'd gotten so late, and then turned back to Donnie, "Try to get some sleep tonight, Donnie!" he called after him.

The purple-masked ninja threw a nonchalant wave over his shoulder, "Right, Leo."

Leo frowned, knowing that the tone his brother had just used was a language all its own – one that basically said "_I will be staying up all night and passing out in front of my laptop. G' night"_.

Swallowing his sigh of frustration, he pinched the bridge of his nose and then turned back to his quarrelling brothers.

"Alright guys – bed, now."

At least he could force two of his three brothers to see reason – or at least, give them something to do aside from kill each other. Well, keep Raph from killing Mikey, who had pulled out a water-balloon from who-knows-where and subsequently drenched the red-banded turtle.

Pulling Raph back away from his younger brother by the shell, Leo walked Raph to his room, discussing the immoral implications of feeding "Mikey-kabobs" to the rats.

* * *

From somewhere farther down the sewer, past a dozen twists and turns, Falco licked his distorted teeth in what may have been glee. His rat servants had just reported the state of the turtle's lair – absolute chaos was the state of things, it sounded. Being the rats they were, his brothers had chewed and weaseled their way into almost every space in the turtle's home – including Donatello's lab.

The reports of the condition of the turtles was even more pleasing than the apparent disarray of their homes. While the attempts to clear out the rats had worn down all four of the turtles, Falco was pleased to hear his assumption had been right – most of the technical work had been left to Donatello to take care of, and it was starting to wear him out. Which was exactly the plan.

It should only take a day or two more, and the brilliant ninja would be too exhausted to defend against a mental offence. Especially since Falco would more than likely catch him off guard, the sleep-deprived turtle's mind would be his for the taking. Then the rest of the pieces would fall perfectly into place, dominos tipping over one at a time.

And then his long-sought revenge would be received.

* * *

**Author's Note:**

Hey guys! This should be updated every 2 or 3 days! This is my first TMNT multi-chapter fic, so please let me know if I should continue. Thanks for reading, hope you liked it!


	2. Home Security

**A Rat in the Sewer**

* * *

Disclaimer: As I'm sure is much to everyone's surprise, I do not own TMNT in any generation or format. I understand if you feel the need to sit down and take a minute to reorient yourself after this devastating news.

* * *

**Chapter Two: Home Security **

Words bled across the screen in a blurry mess, making it hard for Donnie to focus. A head-splitting migraine was slowly emerging, pounding at the back of his eyes, and the light from the computer screen was _unbearable_ – but the worst part of the whole mess was the relentless _squeaking_. It's been _nine_ days of constant, unavoidable _squeaks_ that didn't seem to end. It was literally driving Donatello insane, and in a moment of unfeigned frustration, he slammed his laptop closed and sent his hands flying to his temples in an effort to stop the dull roar in his head. Eyes screwed shut, he leaned back in his chair – but even that felt uncomfortable.

Donnie sighed and learned towards the desk again, pushing the laptop away from him before letting his head fall onto his desk heavily – he felt _awful_. Even his stomach felt as though it was ready to shove everything he'd eaten onto the floor.

"_What is wrong with me?"_ Donnie moaned inwardly. Usually he could handle a few days without sleep without falling through himself like this. It was just how things had always been – sure, he got tired afterwards, of course…but never like this. This was…_terrible_. Light was painful, reading was painful, even thinking – _especially _thinking was just…excruciating.

Loosely, he tried to remember when he'd slept last – but his memories came back empty, save for a three hour nap he'd squeezed in…Donnie's brow furrowed as he tried to remember…two days ago_. Awesome_. Leo would probably chew him out for _that_ later too, which wouldn't help his headache in the slightest.

In his defense, he hadn't had much of a chance to rest. Being the Mr. Fix-It he was, he'd been booked since the first day the rats had decided to take up residence in the lair. Even on day one, the vermin had demolished two pizzas, a headband April had left, and nibbled fringe into Leo's mask. Since then, things had only started to pile up – the blender cord, the toaster, a T-phone; if it was left unattended out in the open, it was on the menu. And then it was on his desk, another item waiting to be repaired and another thing he wouldn't get done.

He groaned to himself again as he dug his face further into arm, which he'd repurposed as a makeshift pillow. Sleep was pulling on his eyelids, and it was a tempting offer. In fact, he started to feel his eyes slowly drooping down…He tried to shake himself awake, but he was fighting a losing battle on multiple fronts. The vague traces of light from the lamp in his room was threatening to sear his eyes shut permanently, the weight of thinking was balancing unevenly in his mind, and the migraine was starting to set in.

"_Maybe I could close my eyes for just a second," _Donnie reasoned with himself warily, "_Just…just for a sec…" _He was exhausted by the time he got the thought out, and he let himself be swallowed into sleep.

* * *

"_Poor, overworked, under-appreciated and exhausted Donatello," A cracked voice whispered, voice oily yet rigid as it glided like over the purple-banded turtle with the smooth but grainy force of rapids._

_Donatello froze – he was…nowhere, really. Literally Wherever it was, whatever kind of place he was in, was simply black. He was standing in the middle of nothing – which was disorienting. No floor, no ceiling, no walls – just blank, empty places. Where…where was he? What kind of dream was this?_

"_Where are you?" The voice laughed coldly, like the though had been clumsy and dull, "Where are you?" he repeated again, this time his voice a chilling chuckle, "Why, Donatello – don't you recognize the recessives of your own mind? And I can assure you that this is no dream, terrapin. Which really is a ignominy – I know you need the rest."_

_Donatello's eyes narrowed, becoming slits as he whipped his head from side to side, reaching for his Bo. In a fluid motion, he had he the staff wrapped tightly in his hands, his grip so constricted that white tips had formed on the top of his knuckles. He had finally recognized the voice._

_It belonged to Dr. Falco; otherwise known as the last person Donnie wanted pursuing his thoughts – which he obviously was. He repressed a shudder, hating that the madman had somehow slunk his way into his mind._

"_Very good, Donatello! Recognizing me by voice? Truly, your mind is one of the more interesting ones I've come across. It's so…complex. So many thoughts – and intricate ones at that," Falco mused before letting his tone drop a few significant degrees as he grinned darkly, "It'll be a such shame when I break it."_

_Suddenly Falco's form appeared in front of the turtle, coming together in a with a veil of smoke. He smiled at Donnie's shocked expression, suppressing a laugh at the turtle drew his staff up defensively, as thought to his him._

"_Oh come now, Donatello," the scientist clicked his teeth together in amusement, his eyes scarlet orbs, "You're smarter than that. You don't honestly expect to land a hit on me _here_ of all places, do you?"_

"_Most of science's greatest discoveries are based trial and error," The turtle grunted in reply, his Bo already flowing through his fingers like solidified water. He twirled the staff with ease, weaving an elaborate pattern before he plunged the front of the staff at Falco's abdomen – but for all his efforts, the onslaught was useless. The Bo sailed straight through his target, like he'd charged the staff through a pillar of smoke. A laugh, icy and cruel, echoed through the vast darkness._

"_I guess," Falco grinned, clearly enjoying himself, "That would fall under the 'error' category."_

_Donnie frowned, replacing his staff in its holder now that it had proved useless. His mind was racing as he stepped back – this man had taken over _Splinter's_ mind. Now…that may have been because he seemed to specialize in rats nowadays, but he still apparently had retained his ability to manipulate thoughts. The point was, if he had gotten his Sensei under his telepathic control, there was a good chance he could get him under his control as well. Donnie needed to be on his guard. Perhaps…-_

"_There you go again!" Falco sounded genuinely amused, his ghostly form creeping ever closer, his eyes snake-like slits as he flowed around Donatello as though he were examining a trophy, "So many plans, so many observations, and in so little time," the man paused, noticing Donnie's eyes glued to him in defensive anger, and he grinned, shaking his head sadly, "It's a pity your family doesn't value your talents."_

_Donnie felt his eyes harden at the comment – so that was his plan._

"_That won't work Falco, if you're trying to get me against the family. They appreciate me," he shot back, taking a step away from the foggy form of the elder scientist._

_Falco tilted his head to the side, a faux wave of sympathy racing into his crimson eyes._

"_Do they, Donatello?"_

_Images sprang through his mind unwillingly, years of memories engulfing him at once – _

"_How can I put this gently?" Raph's voice cut through the air, "We're…better than you."_

"_Dude," Mikey's amused squeal echoed loudly through the spaced, "You're stick exploded!"_

"_Uh, not now, Donnie," Leo was saying rushedly._

_Then the images appeared, life-sized figures of his brothers standing before him._

_First to move was Raph – a vision of him breaking Donatello's staff during practice, and then proceeding to smash the weapon against his shell like the young scientist was a discarded drum set played through the air. Then Mikey's form animated, clutching the carefully constructed smoke bombs in his hands – the ones that had taken _forever_ to make – and he was throwing them against the ground frivolously, erupting into plumes of purple smoke._

"_Er, Mikey-" Donatello began, but then shook his head – this wasn't real…Besides, his brother had just been excited with the new invention. It hadn't been lack of respect._

"_Still trying to defend them?" Falco cooed sadly, and more images rushed around Donnie._

_Raph was standing over him as he worked, trying to figure out how to found Snakeweed – "No, I think hitting will help," Raph intoned threateningly, and Donnie watched his own pencil start to write harder and faster._

_Suddenly the vision changed, and Leo's katanas were grinding blades with a foot ninja's own sword as he looked back at a ghostly memory version of Donnie, who was leaning over the bomb worriedly as Leo yelled, "Let's hurry it up, Donnie!" the leader said hastily._

"_I'm working as fast as I can!"_

"_Then work faster!" Raph was shouting back-_

_Before the rest of the memories could continue, Donnie punched at the smoke forcibly, the images dissipating in a waterfall of foggy curls and then fading altogether. His thoughts were ringing, he felt sick, and his head hurt – like a sledgehammer was dancing on his skull. Combine that with Falco's fog-made memories eating at him, and he could hardly focus._

"_Leave me alone!" Donnie yelled out, turning to face Falso, who was facing him with a gravestone smirk._

"_And for all of you efforts," the older scientist continued darkly, his face now directly up to Donatello's, "What do you get? Nothing. Not even a 'thank you'."_

_Donnie shrunk back, stumbling backwards from the doctor, "I don't need them to tell me the appreciate me! I just _know_." He spat back warily, but the strength behind his voice was ebbing._

"_Mmm-hmm…Maybe," the doctor replied disbelievingly "Or, perhaps they aren't really the ones to blame. I mean, I can understand their hesitation to give you too much praise – with your failures."_

_Donnie gasped as Timothy appeared before him, a screaming blob. Eyes filled with sadness and confusion, the monster roared in pain – and Donnie squeezed his eyes shut, feeling sick._

"_I-I promised I'll fix him up." Donnie murmured, and Falco grinned – the turtle was breaking. Granted, the success was of little accomplishment due to the fact the turtle was exhausted, not totally alert, and he'd been itching away at Donnie's mind for a few hours previous to his falling asleep – but the feeling of victory was potent nonetheless._

"_Oh, and that leads us to your promises. Do you honestly think you'll be able to keep them all? After all, you've already failed the poor boy – what about April? Two times now you've had the chance to save hi, and two times you have failed. How…inadequate." Falco observed reproachfully._

_Donnie's breathing was heavy, and he turned away from the image of April's saddened face that had appeared in front of him._

"_Stop it, Falco." Donnie said harshly, his eyes tightened and anger biting at him – because, even though he knew what the doctor was trying to do, he had a point. Many points, actually. What he really needed was some time to think, some time to-_

* * *

"Donnie?"

Donatello forced his tired eyes open, vision blurry before he finally settled on Leo's concerned face. He lifted his head heavily, glancing around his room – it was still covered in broken appliances and loose wires, and his face was imprinted the indention of the table. Starting to wake up, he wiped away at his face before his vision cleared.

"Eh, I'm awake," he muttered, rubbing at his eyes one last time before turning to Leo curiously, "What's going on?"

Leo's expression was that of worry, and he examined Donnie carefully. His younger brother was obviously tired, and purple bags were starting to form under his brown eyes. He noticed Donnie's skin had paled, and he frowned.

"I was walking past your lab, and I found you asleep on your desk. I've been trying to get you wake up for a few minutes, I guess – you looked like you were having a nightmare," Leo explained, concern growing as he continued, "It was like you were in a comma, Don. You sure you're okay?"

"Fine," Donatello answered curtly as he pinched at the bridge of his nose, the remnants of his dream still filtering throughout his mind – which wasn't helping the migraine.

"Uh…right," Leo replied, not used to such a short answer from his intelligent little brother – if Donnie was working on something, he usually liked to talk things out to someone. Even if they didn't understand it, it seemed to help him figure something out. But the terse reply was out of character, even for the times when Donnie preferred to work things out on his own. Leo paused, figuring something might be wrong.

"So," the leader trailed carefully, eyes landing on the desk, "Is everything here working out okay with this stuff?" He wondered, trying to figure out if it was frustration that was aiding Donnie's bad mood.

Donnie turned on him, and Leo felt surprise leap onto his face when he saw an exhausted but hardened suspicion and anger leap onto the genius's face.

"Is that why you're in here?" Donnie asked offhandedly, his eyes narrowed, "To make sure I'm getting stuff _done_?" He demanded accusingly.

"Er, no-" Leo raised his hands to his chest, palms to Don and fingers outstretched, "I just – I wanted to know how things were going for you."

Donnie was about to snap out a stinging retort, but he grabbed ahold of himself uneasily – he didn't want to yell at Leo. He wasn't mad…well, he hadn't been.

This was Falco talking…or at least, sort of.

Donnie's face fell, and he looked at Leo apologetically, "Sorry Leo," he muttered, digging the heels of his hands into his eyes before standing up, "I just have a headache." He said, walking over to the door, "I'm going to go grab some Tylenol."

Leo watched in confusion as Donnie excused himself, not waiting for Leo's response as he walked out of the room.

"_What was that?" _Leo thought to himself, "_Donnie's never acted like that before...Maybe the stress is getting to him."_


End file.
